Ammar Qurabi heads the National Organization for Human Rights in Syria. He said 13 people were killed in tank shelling on a village outside Daraa, the southern city where the Syrian uprising began in mid-March.

Five others were killed in the central city of Homs.

More than 750 people have been killed in a crackdown on the unrest and thousands of Syrians have been detained since the revolt started.

The Syrian army shelled residential areas in the country`s third-largest city Wednesday, killing at least one person in a sharp escalation in the government`s attempts to crush a popular revolt against President Bashar Assad`s autocratic rule, according to activists and witnesses.

Heavy tank- and gunfire rocked at least three residential neighborhoods in the besieged city of Homs, which has seen some of the largest anti-government demonstrations during the seven-week-long uprising.

"There were loud explosions and gunfire from automatic rifles throughout the night and until this morning," a resident told The Associated Press by telephone, asking that his name not be used for fear of government reprisals. "The area is totally besieged. We are being shelled."

Activists said at least one person was shot dead Wednesday, most likely by snipers, as he was leaving his home in the Bab Amr area. The reports could not be independently confirmed.

More than 750 people have been killed in a crackdown on the unrest and thousands of Syrians have been detained, with about 9,000 still in custody, said Ammar Qurabi, who heads the National Organization for Human Rights in Syria.

Witnesses have reported the shelling of neighborhoods in recent weeks, but the four-hour long siege was the most intense and signaled the government was stepping up its efforts to intimidate the population.

The practice of shelling residential areas is not unprecedented in Syria.

In 1982, Assad`s father, Hafez, crushed a Sunni uprising by shelling the town of Hama, killing 10,000 to 25,000 people according to Amnesty International estimates.

Conflicting figures exist and the Syrian government has made no official estimate. But for the next two decades, until his death, Hafez Assad ruled uncontested and the massacre was seared into the minds of Syrians.

Though Bashar Assad has not done anything on the scale of the Hama massacre in his 11 years in power, his crackdown has evoked memories of his father`s brutal legacy.

He has dispatched army troops backed by tanks to Homs and other communities across the country, saying soldiers and security forces are rooting out "armed terrorist groups" and thugs he says are behind the violence.

Assad also has announced a series of reforms, widely viewed as symbolic overtures to appease protesters since the movement began in the southern city of Daraa in mid-March and quickly spread nationwide.

State-run Syrian TV said Wednesday the government formed a committee to come up with a new election law that would be "up to international standards."

Before the uprising, such a declaration would have been unthinkable in a country with harsh restrictions who is allowed to run. Assad himself inherited power from his father in 2000 after an election in which he was the only candidate.

Also Wednesday, Assad was quoted by Syria`s private Al-Watan newspaper urging Syrians to cooperate with the government so that the reform process may continue. He also pledged a swift solution to the issue of detainees who were jailed during the unrest.

Wednesday`s shelling targeted the Bab Sbaa, Bab Amr and Jouret el Aris neighborhoods, according to activists in Damascus who were in touch with residents in Homs. The city also is home to one of Syria`s two oil refineries.

Syrian television quoted a military official as saying that soldiers and security forces were pursuing "armed terrorist groups" and arrested tens of fugitives and seized large quantities of weapons.

The official, who was not identified, said two soldiers were killed and five wounded during confrontations Wednesday.

The regime has come under increasing international pressure to end its crackdown.

Germany, meanwhile, said several European countries were summoning Syrian ambassadors and threatening new sanctions targeting the country`s leadership if it doesn`t halt the repression of protesters.

The European Union already has decided to impose sanctions on 13 Syrian officials, prohibiting them from traveling anywhere in the 27-nation bloc. But the first round of sanctions doesn`t target Assad himself.

Foreign Ministry spokesman Andreas Peschke said European officials will make clear that "a second package that also includes the Syrian leadership" will follow if Syria does not immediately change course.

U.N. chief Ban Ki-moon also urged Syria Wednesday to allow an international aid assessment team to enter Daraa. He told reporters in Geneva he is disappointed the assessment team "has not yet been given the access it needs."

Ban added he had been assured by Assad that the team would be allowed into the city.

Despite the government crackdown, small demonstrations and candlelight vigils were reported in several areas in the past few days.

Activists said three protesters were killed late Tuesday when government forces fired on demonstrations in Jassem, one of a cluster of villages near Daraa.

In the coastal city of Banias, where the army has also sent soldiers and tanks and arrested hundreds as part of military operation, rights activists said electricity, water and communications have been restored.

Rami Abdul-Rahman, director of the Syrian Observatory for Human Rights, said authorities also released some 300 people Tuesday after making them sign a pledge not to state protests. But he said an army tank was still deployed in the city`s main square were protests were held in past weeks.

Abdul-Rahman said at least seven civilians, including four women, were killed during military operations in the city.